Image Forming Apparatus and Storage Method Capable of Suppressing Occurrence of High-Temperature Offset

This application is based upon and claims the benefit of priority from the corresponding Japanese Patent Application No. 2024-080642 filed on May 17, 2024, the entire contents of which are incorporated herein by reference.

The present disclosure relates to an image forming apparatus and a storage method.

An electrophotographic image forming apparatus includes a fixing portion such as a fixing belt that fixes a toner image transferred onto a sheet to the sheet. In this type of image forming apparatus, when an image is formed on a sheet having a size in the width direction that is smaller than a predetermined reference size, an outer side of a contact area with the sheet in the fixing portion may become excessively hot. In this state, when an image is formed on a sheet with a larger size in the width direction, a defect called high-temperature offset occurs, in which some toner included in a toner image transferred to the sheet is transferred to a subsequent sheet via an excessively heated area in the fixing portion. In response to this, an image forming apparatus is known that prohibits an image forming operation and executes a temperature lowering process to reduce the temperature of the fixing portion when the size in the width direction of the sheet on which the next image is to be formed is larger than the size in the width direction of the sheet on which the previous image was formed.

An image forming apparatus according to a first aspect of the present disclosure includes: a fixing portion, a first storage processing portion, a determination processing portion, a second storage processing portion, a third storage processing portion, and a fourth storage processing portion. The fixing portion fixes the toner image transferred onto the sheet to the sheet. The first storage processing portion stores in a volatile first storage portion width size information corresponding to a size in a width direction of a sheet perpendicular to a conveying direction of the sheet after the sheet has passed a fixing position of the toner image by the fixing portion. The determination processing portion, using the width size information last stored in the first storage portion, determines, in a case in which an image forming process for forming an image on the sheet is executed, whether or not a temperature lowering process for lowering a temperature of the fixing portion is necessary. The second storage processing portion, in a case in which power supply to the first storage portion is stopped, stores the width size information last stored in the first storage portion in a non-volatile second storage portion. The third storage processing portion, in a case in which power supply to the first storage portion is started, stores, in the first storage portion, the width size information that was last stored in the second storage portion. The fourth storage processing portion, after the width size information is stored by the third storage processing portion, stores, in the second storage portion, the width size information corresponding to the size in the width direction of the sheet having a minimum size in the width direction among the sheets on which an image can be formed by the image forming apparatus.

The storage method according to another aspect according to the present disclosure is executed by an image forming apparatus including a fixing portion that fixes a toner image transferred onto a sheet to the sheet and includes: a first storage step, a determination step, a second storage step, the third storage step, and a fourth storage step. In the first storage step, width size information corresponding to a size in a width direction of a sheet perpendicular to a conveying direction of the sheet after the sheet has passed a fixing position of the toner image by the fixing portion is stored in a volatile first storage portion. In the determination step, in a case in which an image forming process for forming an image on the sheet is executed, whether or not a temperature lowering process for lowering a temperature of the fixing portion is necessary is determined using the width size information last stored in the first storage portion. In the second storage step, in a case in which power supply to the first storage portion is stopped, the width size information last stored in the first storage portion is stored in a non-volatile second storage portion. In the third storage step, in a case in which power supply to the first storage portion is started, the width size information that was last stored in the second storage portion is stored in the first storage portion. In the fourth storage step, after the width size information is stored by the third storage processing portion, the width size information corresponding to the size in the width direction of the sheet having a minimum size in the width direction among the sheets on which an image can be formed by the image forming apparatus is stored in the second storage portion.

This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description with reference where appropriate to the accompanying drawings. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Furthermore, the claimed subject matter is not limited to implementations that solve any or all disadvantages noted in any part of this disclosure.

Hereinafter, embodiments according to the present disclosure will be described with reference to the accompanying drawings. Note that the following embodiments are examples that embody a technique according to the present disclosure, and do not limit the technical scope of the present disclosure.

[Configuration of Image Forming Apparatus]

First, a configuration of an image forming apparatusof an embodiment according to the present disclosure will be described with reference to.

Note that for ease of explanation, a vertical direction in an installed state in which the image forming apparatusis usable (the state shown in) is defined as an up-down direction D. In addition, a front-rear direction Dis defined with the left side of the paper surface of the image forming apparatusshown inbeing the front (front surface). Moreover, a left-right direction Dis defined based on the front of the image forming apparatusin the installed state.

The image forming apparatusis a multifunction peripheral having multiple functions, such as a scanning function for reading an image of an document sheet, a printing function for forming an image based on image data, a fax function, and a copy function. Note that the present disclosure may be applied to image forming apparatuses such as printers, fax machines, and copiers.

As shown in, the image forming apparatusincludes an auto document feeder (ADF), an image reading portion, an image forming portion, a sheet feeding portion, an operation display portion, a storage portion, and a control portion.

The ADFconveys an document sheet to be read by the scanning function. The ADFincludes a document sheet setting portion, a plurality of conveying rollers, a document sheet holder, and a sheet discharge portion.

The image reading portionimplements the scanning function. The image reading portionincludes a document sheet table, a light source, a plurality of mirrors, an optical lens, and a charge coupled device (CCD).

The image forming portionimplements the printing function. More specifically, the image forming portionforms a color or monochrome image on a sheet supplied from the sheet feed portionaccording to an electrophotographic method.

The sheet feed portionsupplies sheets to the image forming portion. The sheet feed portionincludes a sheet feed cassette, a manual feed tray, and a plurality of conveying rollers.

The operation display portionis a user interface of the image forming apparatus. The operation display portionhas a display portion such as a liquid-crystal display that displays various types of information in response to control instructions from the control portion, and an operation portion such as operation keys or a touch panel that inputs various types of information to the control portionin response to user operations.

The storage portionis a non-volatile storage device. For example, the storage portionis a flash memory. The storage portionis an example of a second storage portion according to the present disclosure.

The control portionperforms overall control of the image forming apparatus. As shown in, the control portionincludes a CPU, a ROM, and a RAM. The CPUis a processor that executes various types of arithmetic processing. The ROMis a non-volatile storage device in which information such as control programs for causing the CPUto execute various types of processes is stored in advance. The RAMis a volatile storage device used as a temporary storage memory (work area) for various types of processes executed by the CPU. The CPUperforms overall control of the image forming apparatusby executing various types of control programs prestored in the ROM. The RAMis an example of a first storage portion according to the present disclosure.

Note that the control portionmay be a control portion provided separately from a main control portion that performs overall control of the image forming apparatus. In addition, the control portionmay also be configured with an electronic circuit such as an integrated circuit (ASIC).

Next, a configuration of the image forming portionwill be described with reference to. Here,is a cross-sectional view showing a configuration of a plurality of image forming units, the intermediate transfer belt, and the secondary transfer roller.

As shown in, the image forming portionincludes four image forming units, a laser scanning unit, an intermediate transfer belt, a secondary transfer roller, a fixing device, and a sheet discharge tray.

Of the four image forming units, the image forming unit(see) forms a yellow (Y) toner image. Of the four image forming units, the image forming unit(see) forms a cyan (C) toner image. Of the four image forming units, the image forming unit(see) forms a magenta (M) toner image. Of the four image forming units, the image forming unit(see) forms a black (K) toner image. That is, the image forming portionforms an image on a sheet using each of the CMYK toners. As shown in, the four image forming unitsare arranged side by side in the order of yellow, cyan, magenta, and black from the front side of the image forming apparatusalong the front-rear direction D.

As shown in, each image forming unitincludes a photoconductor drum, a charging roller, a developing device, a primary transfer roller, and a drum cleaning portion. In addition, each of the image forming unitsalso includes a toner containershown in.

An electrostatic latent image is formed on a surface of the photoconductor drum. For example, the photoconductor drumhas a photosensitive layer made of amorphous silicon. The photoconductor drumreceives a rotational driving force supplied from a motor (not shown) and rotates in a rotational direction Dshown in. Thus, the photoconductor drumconveys the electrostatic latent image formed on the surface.

The charging rolleris applied with a preset charging voltage to charge the surface of the photoconductor drum. For example, the charging rollercharges the surface of the photoconductor drumto a positive polarity. The surface of the photoconductor drumcharged by the charging rolleris irradiated with light based on image data emitted from the laser scanning unit. Thus, an electrostatic latent image is formed on the surface of the photoconductor drum.

The developing devicedevelops the electrostatic latent image formed on the surface of the photoconductor drum. The developing deviceincludes a pair of stirring members, a magnetic roller, and a developing roller. The pair of stirring members stir developing agent contained inside the developing device. The developing agent includes a toner and a carrier. Thus, the toner contained in the developing agent is charged to have a positive polarity due to friction with the carrier contained in the developing agent. The magnetic roller picks up the developing agent stirred by the pair of stirring members, and supplies the toner contained in the developing agent to the developing roller. The developing roller conveys the toner supplied from the magnetic roller to a position facing the photoconductor drum. In addition, the developing roller receives a preset developing bias voltage and supplies the toner conveyed to the opposing position to the photoconductor drum. Thus, the electrostatic latent image formed on the surface of the photoconductor drumis visualized (developed). The developing deviceis supplied with toner from a toner container.

The primary transfer rolleris supplied with a preset primary transfer current, and transfers the toner image formed on the surface of the photoconductor drumonto an outer peripheral surface of the intermediate transfer belt. As shown in, the primary transfer rolleris provided opposite the photoconductor drumwith the intermediate transfer beltinterposed therebetween.

The drum cleaning portionremoves the toner remaining on the surface of the photoconductor drumafter the toner image has been transferred by the primary transfer roller.

The laser scanning unitemits light based on image data toward the surface of the photoconductor drumof each image forming unit.

The intermediate transfer beltis an endless belt member onto which toner images formed on the surfaces of the photoconductor drumsof the image forming unitsare transferred. The intermediate transfer beltis stretched with a predetermined tension by a drive rollerA (see) and a tension rollerB (see). The intermediate transfer beltrotates in a rotation direction Dshown inas the drive rollerA rotates upon receiving a rotational driving force supplied from a motor (not shown). Thus, the intermediate transfer beltconveys the toner image formed on the outer peripheral surface to a secondary transfer position P(see) where the secondary transfer rollertransfers the toner image. Note that after the toner image is transferred by the secondary transfer roller, the outer peripheral surface of the intermediate transfer beltis cleaned by the belt cleaning deviceC shown in.

The secondary transfer rolleris supplied with a preset secondary transfer current, and transfers the toner image transferred onto the outer peripheral surface of the intermediate transfer beltonto a sheet supplied from the sheet feed portion. As shown in, the secondary transfer rolleris provided opposite the drive rollerA with the intermediate transfer belttherebetween. The secondary transfer rolleris pressed toward the drive rollerA by a pressing member (not shown) so as to come into contact with the intermediate transfer beltwith a predetermined nip pressure. The secondary transfer rollertransfers the toner image formed on the intermediate transfer beltonto a sheet at a secondary transfer position P(see) where the secondary transfer rollercomes into contact with the intermediate transfer belt. The sheet onto which the toner image has been transferred at the secondary transfer position Pis conveyed in a conveying direction D(see) toward a fixing position P(see).

The fixing devicefixes the toner image transferred onto the sheet by the secondary transfer rollerto the sheet.

The sheet on which the toner image has been fixed by the fixing deviceis discharged to a sheet discharge tray.

Next, a configuration of the fixing devicewill be described with reference to.

As shown in, the fixing deviceincludes a fixing belt, a heater, a heater support portion, a pressing member, and a pressure roller. In addition, as shown in, the fixing devicealso includes a temperature sensorand a motor.

The fixing beltfixes the toner image transferred onto the sheet to the sheet. The fixing beltis an example of a fixing portion according to the present disclosure. Note that the fixing portion according to the present disclosure may be a member having a shape different from that of a belt, such as a fixing roller.

As shown in, the fixing beltis a member formed in a shape of an endless belt. The fixing beltis flexible. The fixing beltis sandwiched between a heaterand a pressure roller, and runs along a running direction D(see) following the rotation of the pressure roller. The sheet onto which the toner image has been transferred is heated and pressed when passing through a fixing position P(see) where the toner image is fixed by the fixing belt. Thus, the toner image transferred onto the sheet is fixed to the sheet. Fixing position Pis a position where the fixing beltand the pressure rollercome into contact with each other.

The heaterheats the fixing belt.

The heateris formed in a flat plate shape extending in the left-right direction D. The heateris provided in contact with an inner peripheral surfaceB of the fixing belt(see).

As shown in, the heaterincludes a substrateC and a resistive heating elementD. The substrateC is formed in a flat plate shape extending in the left-right direction D. The resistive heating elementD is mounted on a first surfaceA (see) of the substrateC that contacts the inner peripheral surfaceB of the fixing belt. The resistive heating elementD is connected to a power supply (not shown) via a wiring pattern or the like mounted on the first surfaceA. The resistive heating elementD generates heat when a current supplied from the power supply flows therethrough.

The heateris provided opposite the pressure rollerwith the fixing belttherebetween. In addition, by pressing the heatertoward the pressure rollerside by the pressing member, the heateris brought into pressure contact with the inner peripheral surfaceB of the fixing belt.

The heater support portionsupports the heater. As shown in, the heater support portionis formed with a recess portionA into which the heatercan be fitted. The heateris fitted into the recess portionA of the heater support portion.

In addition, the heater support portionguides the fixing beltso that the fixing beltruns along a predetermined running path. More specifically, the heater support portionincludes a pair of guide portionsB (see) that contact the inner peripheral surfaceB of the fixing beltand guide the fixing belt.

The pressing memberpresses the heater support portiontowards the pressure rollerside. The pressing memberis provided in contact with the heater support portionand is elongated in the left-right direction D, which is the width direction of the fixing belt. In addition, both ends in the longitudinal direction of the pressing memberreceive a pressing force from a pressing member (not shown) in a direction toward the pressure rollerside. Thus, the pressing memberpresses the heater support portiontowards the pressure rollerside. When the heater support portionis pressed toward the pressure rollerside, the heatersupported by the heater support portionis also pressed toward the pressure rollerside.

The pressure rolleris provided in contact with the outer peripheral surfaceA of the fixing belt. The pressure rollerincludes a metal shaft portionA and an elastic layerB having elasticity formed on the outer periphery of the shaft portionA. The shaft portionA is rotatably supported by a pair of side plates provided inside a housing of the image forming apparatus. The pressure rollerreceives a rotational driving force supplied from the motorand rotates in a rotational direction D(see).

The temperature sensordetects the temperature of the heater.

As shown in, the temperature sensoris provided on a second surfaceB of the heateron a rear side of the first surfaceA. For example, the temperature sensoris an electrical circuit including a thermistor, and outputs an electrical signal according to the temperature at the installation position. The electrical signal output from the temperature sensoris input to the control portion.

The motorsupplies a rotational driving force to the pressure roller.

In the image forming apparatus, in a case in which an image is formed on a sheet having a size in the width direction that is smaller than a predetermined reference size, the temperature of the fixing beltoutside the contact area with the sheet may become excessively high. In this state, when an image is formed on a sheet having a larger size in the width direction, a defect called high-temperature offset occurs, in which part of the toner contained in the toner image transferred to the sheet is transferred to the subsequent sheet via an excessively heated area of the fixing belt. In response to this, an image forming apparatus is known that prohibits an image forming operation and executes a temperature lowering process to reduce the temperature of the fixing beltwhen the size in the width direction of the sheet on which the next image is to be formed is larger than the size in the width direction of the sheet on which the previous image was formed.